1. Field of the Invention
The present invention relates to a turbofan, and more particularly, to a turbofan and a mold manufacturing the same.
2. Background of the Related Art
Generally, a turbofan is a kind of centrifugal fan sending air forcibly by a centrifugal force of air generated from revolution of an impeller thereof. The turbofan produces massive airflow so as to be suitable for a refrigerator of heavy capacity.
FIG. 1 illustrates a layout of a turbofan according to a related art, and FIG. 2 illustrates a vertical cross-sectional view of the general turbofan in FIG. 1.
Referring to FIG. 1 and FIG. 2, a turbofan 1 according to a related art includes a hub 10 having a boss 11 at a central part so as to be coupled with a rotational shaft 40 of a driving device (not shown in the drawings), a plurality of blades 20 at a circumferential part 10a of the hub 10, and a shroud 30 arranged at a opposite face to the hub 10 so as to be coupled with the blades in one body wherein the blades 20 are inserted between the shroud 30 and the hub 10.
An internal diameter increases toward the hub 10 in a direction of the rotational shaft 40, and has a concave shape. A cross-section of each blade 20, as shown in FIG. 1, has an airfoil figure.
The above-constructed turbofan 1 according to the related art is mainly manufacture by injection molding of synthetic resin. The blades 20 and hub 10 are formed in one body, but the shroud 30 is molded separately. Theses parts are assembled reciprocally so as to complete the turbofan 1.
When the turbofan is manufactured by the above process, the number of molding patterns increases, whereby consumes time and expense excessively. Besides, the above process needs a step of assembling separate parts, thereby extending a manufacturing time to increase the overall product cost.
In order to overcome the above disadvantages or defects, a process of manufacturing a turbofan is lately used so as to reduce the number of molding patterns and skip an auxiliary assembling step. Namely, in the latest process, a maximum outer diameter d1 of the hub 10 is reduced to a size less than a minimum inner diameter d2. And, longitudinal boundary surfaces (BSL) of upper and lower molding patterns are formed to have an inner diameter equal to the maximum outer diameter d1 so as to assemble the hub 10, blades 20, and shroud 30 in one body reciprocally.
FIG. 3 illustrates longitudinal cross-sectional views of a turbofan and a molding pattern to manufacture a turbofan, and FIG. 4 illustrates a magnified cross-sectional view of the assembly of the molding pattern in FIG. 3.
Referring to FIG. 3 and FIG. 4, a molding pattern for forming a turbofan according to a related art includes a lower molding pattern part 50 arranged to be fixed to a lower part in a direction of a rotational shaft 40 and having a molding surface inside to form a partial area of a hub 10 and blades 20 and an upper molding part 60 having a molding surface inside to form the rest area of the shroud 30 and blades 20 and providing a space to form the turbofan 1 by being assembled with the lower molding part 50.
A hub molding part 61 recessed in a direction of the rotational shaft 40 is formed at a central part of the molding surface of the upper molding pattern part 60 so as to form the hub 10. And, a boss molding part 62 is formed at a central part of the hub molding part 61 so as to mold the boss 11. Along a radial direction of the rotational shaft 40, a blade molding part 63 is formed at an external side of the boss molding part 62 so as to form the blade 20 in part. Along a direction of the rotational shaft 40, a shroud molding part 64 is formed over the blade molding part 63 so as to form an upper surface of the shroud 30.
Meanwhile, a hub molding part 51 protrudes out of the central part of the upper surface of the lower molding pattern part 50, and a boss molding part 52 is formed at a central part of the hub molding part 51. Along a radial direction of the rotational shaft 40, a blade molding part 53 is formed at an external side of the hub molding part 51 so as to mold the rest of the parts of the blades 20. And, a concave shroud molding part 54 is formed at an upper part of the blade molding part 53 so as to form a lower surface of the shroud 30.
In order to manufacture the above-constructed turbofan, when the upper molding pattern part 60 is tightly coupled with the lower molding pattern part 50, a molding space to form the turbofan constructed with the hub 10, blades 20, and shroud 30, which are built in one body, is provided inside the lower and upper molding pattern parts 50 and 60. A molten synthetic resin is then injected in the molding space for the turbofan. After the injected synthetic resin has been hardened, the upper and lower molding pattern parts 60 and 50 are separated from each other as well as the turbofan 1 is separated, the turbofan having the hub, blades 20 and shroud 30 formed in one body is manufactured.
In the turbofan according to the related art, the inner diameter of the shroud 10 increases when getting closer to the hub 10 along a direction of the rotational shaft 40 so as to guide airflow with the hub 10. Thus, a cross-section of the shroud 10 is concave. In the molding pattern for form the shape of the shroud 30, the longitudinal boundary surface BSL, at which the lower and upper molding pattern parts 50 and 60 meet each other, is formed along the direction of the rotational shaft 40, and an edge 55 is formed at a contact between the longitudinal boundary surface BSL and the shroud molding part 54 of the lower molding pattern part 50. Such a sharp edge 55, when being contacted with the upper molding pattern part 60, is damaged or distorted by a relatively small external force with ease. Hence, durability of the molding pattern is shortened so as to need a replacement frequently. Thus, the turbofan according to the related art increases cost of product.